The present invention relates to methods and apparatus for manufacturing multilayer paper board.
In particular, the present invention relates to a method and machine for manufacturing a multilayer paper board which includes an outer web for the resulting cardboard and a base web which is bonded to the outer web.
A considerable favorable experience has been gained from the wire section of a paper machine constructed in accordance with the principles of U.S. Pat. No. 3,846,233. This wire section has proved to be a success in the manufacturing at relatively high speed of various paper grades containing mechanical pulp and fillers. Thus, one of the purposes of the present invention is to exploit the favorable experience gained from the above patent. The principles of the invention are applicable to that field of paper manufacturing which relates to the manufacture of cardboard.
Thus, the present invention relates to methods and apparatus for producing multilayer cardboard. Examples of such cardboard grades are boxboard, carton board and foot-container board. Such cardboard grades can be made, for example, on a triple wire machine in which the webs forming on three Fourdrinier sections are bonded to each other in order to produce a cardboard web of a desired substance. Furthermore, cardboard of this type can be made by machines on which some of the component web layers are made on pick-up cylinders while only a single layer is made on a Fourdrinier wire. Such a Fourdrinier wire section is beneficial with respect to the quality of the cardboard but has the disadvantage of occupying a relatively large amount of space. The wet end formed on a pick-up cylinder is highly advantageous with respect to the utilization of space, but production on such a pick-up cylinder of, for example, a transversely even web of good formation is much more difficult to achieve than would be the case with a Fourdrinier. With respect to formation of webs on a pick-up cylinder, it is extremely difficult to regulate the fiber orientation. On such pick-up cylinders fibers easily tend to settle in the running direction of the machine, which is to say in the direction in which the web flows. This latter phenomenon, which affects the strength and stiffness of the board and which in particular causes a deterioration of transversal stiffness, is highly deterimental in cardboard which is required to be used, for example, in the making of boxes. Furthermore, a web formed on a pick-up cylinder tends to become one-sided, and this factor may hinder the utilization of cardboard at numerous conversion stages.